1. Field of the Invention
This invention relates, generally, to wind turbines. More particularly, it relates to a high-efficiency vertical wind turbine.
2. Description of the Prior Art
As the cost of fossil fuels rises and their harmful effects on the environment come to forefront of global attention, alternative sources of energy grow in importance. One source of clean sustainable energy is wind. Humans have been harvesting the power of the wind for numerous applications for millennia. In the recent decades, wind turbines have become a significant source of electricity for many areas, and they are quickly becoming more widespread.
All wind turbines may be subdivided into two classes: horizontal axis wind turbines (HAWT) and vertical axis wind turbines (VAWT). Although a number of VAWT are known in the art, prevalent majority of the currently operating wind turbines are HAWT.
Conventional HAWTs have a number of serious flaws. The blades of a conventional HAWT must always be facing the wind, which requires a control mechanism to continuously adjust the blades to achieve ideal efficiency. This increases the complexity of the design, which results in higher manufacturing and maintenance costs and a higher risk of failure. The blades of a HAWT rotate slowly in a vertical plane about a horizontal axis, and a speed-increasing gearbox is therefore required to connect the slowly rotating blades to a power generator. The presence of a gearbox introduces additional frictional forces into the structure that reduce the power produced by the generator and also requires inverters between the generator and the power grid.
Conventional blades also have little self-start capacity. As a result, energy has to be applied to the blades to re-start their rotation after an interval of no or low wind conditions. Moreover, the large cantilevered design puts strong force moments on bearings with resultant energy loss and noise. Large forces are created by such conventional designs, and large forces lead to high maintenance and high overhead costs. The large surface area of conventional blades creates problems in high wind conditions, creating even more maintenance issues. Furthermore, the complexity of HAWT designs requires a large number of moving parts, therefore increasing the risk of mechanical failure. High fabrication cost, high assembly cost, and high maintenance cost increase the price of the energy produced, making wind energy a less lucrative option.
Other shortcomings of HAWTs are associated with long rotating blades interfering with radars. Long continuously rotating blades constantly ping radars and cause problems with radar coverage, which may be especially problematic for turbines positioned in open waters where vessels and aircraft heavily rely on radars.
Although a number of VAWT designs are known in the art, they are also flawed. The two main types of VAWTs are Darrieus and Savonius. Darrieus VAWT design was first disclosed in U.S. Pat. No. 1,835,018. Darrieus design generates electricity by utilizing symmetrical airfoils which move in a circular path when the wind is present. A major advantage of Darrieus turbine is that unlike conventional HAWT designs, Darrieus design can operate in the airflow of any directions without necessitating adjustment due to changes in the wind direction. However, Darrieus turbine is not self-starting, which means that when the turbine is stationary, there is not net rotational force even when the wind speed rises. Accordingly, a starting device is necessary to bring Darrius turbine into operation each time the wind stops and picks up again.
Another type of VAWTS are Savonius turbines. This design is fairly simple and comprises a number of vertically-mounted airfoils on a rotating shaft. VAWTs built according to Savonius design are self-starting and require considerably less maintenance than other designs. These advantages, however, come at a steep price of greatly reduced efficiency.
Accordingly, there is a need for economical wind turbines that rotate in a horizontal plane about a vertical axis, have good self-starting capacity, require no gearbox, and which incorporate advances in magnetic bearing strength and shape to minimize frictional loss. There is also a need for an improved wind turbine design that reduces pinging or scrambling of sensitive radar signals.
However, in view of the art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the art how the needed improvements could be provided.